The present invention relates to a circular knitting machine and particularly to the feeding of thread to said machine to manufacture tubular knitted items such as socks or stockings, and relates to a device for positioning the feed threads at the needle holders of the active needles of a double-cylinder machine.
Double-cylinder circular knitting machines generally essentially comprise two coaxial rotating cylinders which are both provided, at their outer cylindrical surface, with respective multiple longitudinal slots.
Respective needles are guided in the slots and form the loop of knitting during their vertical stroke by cooperating with the sinkers.
The slots of the cylinders are equal in number to the needles that slide within them with a reciprocating vertical motion and are swapped between the two cylinders: in order to manufacture stockings in general there may be up to approximately 400 slots per cylinder, whereas for the manufacture of men's socks the number of needles is generally between 84 and 280.
The needles are fed, in their reciprocating vertical motion, in fixed angular positions and at the most protruding levels of their strokes with respect to the cylinder on which they are located, by feeder stations which provide, each time, the needles with the feed thread that must be knit in the portion of knitting being formed, in that specific row of knitting and in that specific angular position: every time the feed changes, it is necessary to replace the previously fed thread with the thread that constitutes the new feed.
Each feed thread is carried by a thread guide which takes the thread from a spool: the various thread guides are arranged at mutually different levels and/or radial distances so that their paths do not interfere and so that a thread guide can move its thread to knit without preventing another thread guide from removing its thread from knitting.
In thread guide actuation devices, which often comprise crank-and-rod systems, the end of the thread guide usually follows a specific, usually curved, path which is always the same to move it from an inactive position A to a position B in which it places the thread close to the cylinder and vice versa: in conventional devices there is the drawback that each thread guide can position its thread only in a preset position of the path of the needles, thereby causing a certain stiffness in textile production.
In order to achieve greater freedom in knitting and higher reliability, it would instead be useful to be able to vary, within a certain range, for example 10-20 needle pitches, the point where the new thread is positioned: this possibility becomes very important, with particular reference to the production of sports socks, for feeding the elastic thread and for the initial thread for each new sock.
In particular, with respect to the usual path that moves the end of the thread guide from a retracted inactive position A to the advanced position B for positioning the thread proximate to the cylinder, in order to feed the initial thread of the tube of knitting the end of the thread guide must move to an even further advanced position C and then move to the conventional advanced position B and subsequently follow the usual path: in order to feed the elastic thread, the thread guide must instead first position the thread in B and then move to a position D that is retracted with respect to B.
Currently used devices that meet this requirement are, in some solutions (in which the entire thread guide assembly moves parallel to itself), particularly bulky, whereas other solutions that act on the movable end arm of the thread guide have been found to be subject to jamming and malfunctions.